When exploring for or developing new oil and gas reservoirs, the borehole of a well high on a structure may not penetrate the hydrocarbon/water contact. This contact level should be determined to locate delineation wells, plan development drilling, and forecast reserves and economics, especially when operating in high-cost areas.
In principal, hydrocarbon/water levels can be predicted from a combination of capillary pressure data, and log or core derived porosity .phi., water saturation S.sub.w, and air permeability k. The J-curve correlation presented in a paper by M. C. Leverett entitled "Capillary Behavior in Porous Solids" published in Trans AIME, Vol. 142, pp 151-69, 1941, was developed for unconsolidated sand packs, and was the earliest method proposed to relate laboratory data of capillary pressure P.sub.c, water saturation S.sub.w, porosity .phi. and air permeability k.
Later R. P. Alger, et al. in a paper entitled "New Unified Method of Integrating Core Capillary Pressure Data with Well Logs" and published by SPEFE, pp 145-52 in June 1989 employed a multilinear regression approach to relate these same properties to both core and log data. More recently, D. Smith in an article entitled "How to Predict Down-Dip Water Level" published in World Oil, pp 85-88 in May 1992 predicted the water level from logs with a method for generating synthetic mercury capillary pressure P.sub.c curves if no actual capillary pressure P.sub.c data are available.
The above methods have had only limited success for several reasons. First, laboratory measured capillary pressure data specific to the reservoir are usually not available. Second, to describe the entire reservoir, great care is required for integrating the laboratory capillary pressure data from a few core measurements with log data. Further, if the wells in the reservoir are high above the transition zone, a small error in water saturation produces a large error in the predicted water table. Thus, prior methods are highly sensitive to certain errors that can result in large errors in the predicted water level.